We will continue our studies of the molecular genetics of Simian Virus 40 and human adenoviruses, protein-nucleic acid interactions of restriction and modification enzymes with their recognition sites in DNA, enzymatic repair of damaged DNA, and the regulation of gene expression in rodent liver. Regulatory mutants of SV40 will be characterized; viral and cellular proteins involved in adenovirus DNA replication in vitro will be identified; large amounts of endo R-Hha II, of its companion methylase, and of exonuclease III will be prepared for structural studies of these enzymes.